docs: CLI one-liners for every client that has one

codex mcp add --url + codex mcp login (native streamable HTTP, verified
against the installed CLI; mcp-remote bridge kept for older versions),
gemini mcp add --transport http, code --add-mcp, and a one-click Cursor
install deeplink. Windsurf/Antigravity marked honestly as config-only —
no CLI exists.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>